a) Field of the Invention
The present invention relates to a tone synthesizer for synthesizing a tone of an acoustic musical instrument.
b) Description of the Related Art
Such a tone synthesizer is known which electrically simulates a mechanism for generating a musical tone in an acoustic musical instrument. A tone synthesizer adapted for synthesizing a musical tone of a wind instrument, for example, comprises an exciting circuit for generating a driving waveform signal corresponding to pressure change in a mouthpiece, and a resonance circuit simulating characteristics of a resonance tube which responds to pressure change in the mouthpiece of the wind instrument. A cylindrical resonance tube can be simulated by a transmission circuit called a wave-guide usually constituted by a loop circuit which comprises a delay circuit and a filter. The transmission circuit receives a driving waveform signal from an exciting circuit and outputs a signal of a certain frequency range after amplifying the signal and repeatedly circulating the signal in the loop of the transmission circuit.
A wind instrument such as a saxophone or a trumpet has a conical resonance tube, which in general is considered equivalent to a number of cylindrical short resonance tubes having different diameters and connected in series in the order of the magnitude of the diameter. Consequently, a conical tube is usually simulated by a resonance circuit comprising a plurality of wave-guides and junctions cascading the wave-guides one by one. A tone synthesizer having such a resonant circuit is disclosed, for example, in Japanese Patent Publication Laid-open Nos. Sho-63-40199 and Hei-3-235997.
In order to faithfully simulate a transfer function of a conical resonance tube by a resonance circuit described above, it is necessary to connect many stages of the combination of a waveguide and a junction. Generally, a junction comprises a multiplier for multiplying the input, which is usually large in size. Thus, a conventional resonance circuit comprising a number of Junctions for simulating a wind acoustic instrument with a conical resonance tube is usually large in size.
In order to maintain a similar tone color at different tone pitches, it is necessary to keep the shape of a flared or conical tube in similar shapes. For simulating such similar shapes, it is necessary to control the coefficients of junctions representing cylindrical resonance tubes of different diameter in connection with the tone pitch (delay length). Thus, the control becomes complicated and the circuit scale becomes larger.
In order to simulate a conical resonance tube by a digital signal processor (DSP) executing a certain program in place of an electronic circuit comprising a number of transmission circuits as described above, the amount of processing per unit time the DSP should handle becomes large. It is, therefore, necessary to employ a high speed DSP. Hence, the cost of the DSP increases.